This invention relates to an improved process for the preparation of unsaturated nitriles from corresponding unsaturated olefins by the reaction of ammonia, oxygen and the unsaturated olefin in a fluidized bed catalytic reactor. In particular, the invention is directed to an improved process for the preparation of acrylonitrile by the reaction of ammonia, propylene and oxygen in a fluidized bed catalytic reactor.
The direct ammoxidation of an unsaturated olefin to its corresponding unsaturated nitrile in a fluidized bed reactor is well known. In particular, the production of acrylonitrile by the reaction of ammonia, propylene and oxygen using fluidized bed catalytic reactors is a widely practiced commercial process developed and commercialized by the assignees of the present invention and referred to worldwide as the Sohio Acrylonitrile Process. The process is carried out in a fluidized bed reactor wherein the reactants are passed upwardly through a suitable catalyst and the products and any unreacted starting materials are removed from the top of the reactor. The catalyst used in these processes have been fully described in various U.S. Pat. Nos. 3,642,930; 4,863,891; and 4,767,878 herein incorporated by reference.
A problem associated with the Sohio Acrylonitrile Process has been the nitriding of the feed conduits used to introduce the amrionia into the fluidized bed reactor. It has been observed that over the passage of time, the ammonia feed conduits for the fluidized bed reactor are subject to nitriding (the reaction of monoatomic nitrogen with the metal surface of the feed conduit/sparger) resulting in the metal itself becoming brittle and subject to mechanical failure. This problem has required replacement of the conduits/spargers on a regular basis to maintain the integrity of the apparatus. Over the years, many solutions to the nitriding problems associated with the operation of the Sohio Acrylonitrile Process have been proposed including replacement of the metal conduits or spargers with specific material which is not prone to nitriding. However, this solution has not been completely successful due to other problems associated with the use of nitride resistant material in the environment of the fluidized bed reactor while making acrylonitrile as well as the cost associated with use of these materials.
The problem of nitriding of metals in other environments has been known for many years as evidence by U.S. Pat. Nos. 3,704,690; 4,401,153; 5,110,584; and EPO Patent 0 113 524. These patents each is directed to solutions to the nitriding problem which include the use of nitride resistant alloys. The present invention is directed to a solution to the nitriding problem associated with the Sohio Acrylonitrile Process which does not necessarily incorporate the use of nitriding resistant material.